1. Field of the Invention
The present invention relates to a layout of dummy patterns. More particularly, the present invention relates to a layout of dummy patterns in a pad layer.
2. Description of Related Art
Generally speaking, semiconductor process can be roughly classified into front end process and back end process, wherein front end process includes processes such as formation of substrate, the deposition of film layers, lithography, etching, ion implantation, and metallic interconnects, and back end process is packaging process. Solder pads are formed on the substrate of the semiconductor before entering back end process to be used as signal joints for transmitting circuit signals of the IC to external circuit.
Presently, aluminum, copper, or other alloys are used for manufacturing solder pad. Wherein, copper solder pad has such advantages as low resistance, good anti-electromigration performance, and is ideal for dealing with high device integration. However, copper solder pad is easily destroyed during testing since the hardness thereof is low, and moreover, copper can be easily oxidized, extruded, contaminated, or diffused since copper is very active, which may cause problems during the step of bonding, or require additional cleaning step. Thus, aluminum is usually used as the material of solder pad.
In the conventional technology, to form aluminum pads, an aluminum film layer is first formed and then the aluminum film layer is processed with plasma etching. The proportion of the aluminum pads to the entire aluminum film layer is between 3%˜6%, that is, large amount of the plasma gas needs to be used for removing large areas of aluminum film. Because of the pattern density of the aluminum pad is low, and that the etching machine used in general process is usually designed to etch film of high pattern density, a problem of insufficient process window is occurred of during the etching process of the aluminum pad. Accordingly, the dissociative plasma gas assembles around the aluminum pad pattern, which results in the problem of aluminum erosion and low reliability of the device.
In particular, the material of the aluminum pads is usually aluminum copper alloy containing trace copper, the more aluminum film to be etched and removed, the higher the probability of copper separate out is, thus, defects on the wafer are increased.